Australia’s highest court has declared Family First’s Lucy Gichuhi is South Australia’s new senator.

Lawyer and Family First member Lucy Gichuhi

Labor has lost a last-minute bid to stop Kenyan-born lawyer Lucy Gichuhi being formally declared as South Australia’s new senator.

Labor wanted the declaration delayed so it could argue issues about Ms Gichuhi’s Kenyan citizenship meant she was not eligible to take the vacancy created after Bob Day was ruled ineligible to stand at last year’s federal election.

But the High Court, sitting as the Court of Disputed Returns, said the challenge from former Labor senator Anne McEwen came too late.

Justice Geoffrey Nettle refused Labor’s application on Wednesday, saying issues about Ms Gichuhi’s Kenyan citizenship had been referred to during court hearings over the last three months.

“There has been nothing at all since at least January of this year precluding Ms McEwen from forming the basis of her application or from assembling expert material with which to support it,” Justice Nettle said.

He said it was incumbent on Ms McEwen to arm herself with that information within a reasonable time and she had not done so.

Ms Gichuhi became an Australian citizen in July 2001 after migrating from Kenya in 1999.

Ms McEwen’s barrister Jeremy Kirk SC said there were questions about whether Ms Gichuhi retained Kenyan citizenship despite becoming an Australian citizen, and if so, if she took reasonable steps to renounce it.

Mr Kirk said the issue only truly arose after the court ruled Mr Day ineligible and Ms Gichuhi won last Thursday’s special recount of votes.

He had argued the court should not declare Ms Gichuhi, a Family First candidate like Mr Day, duly elected given the real questions about her eligibility.

Mr Kirk said without considering the issue of Ms Gichuhi’s eligibility, the court’s declaration could be called into question.

Commonwealth solicitor-general Stephen Donaghue QC said while the special count only took place last Thursday, it had long been foreseeable that if Mr Day was ruled ineligible his replacement would likely be Ms Gichuhi.

Ms Gichuhi had declared she became an Australian citizen in 2001 and was eligible to be elected as a senator, he said.

Mr Donaghue said under the Kenyan constitution, a person ceased to be a citizen if they were aged over 21 and voluntarily acquired the citizenship of another country.

“On the material presently available it is difficult to see how there is an issue,” Mr Donaghue said.

The Kenyan High Commission had also provided a letter stating that Ms Gichuhi was not regarded as a Kenyan citizen, he said.

Acting shadow attorney-general Katy Gallagher had said Labor had believed there were legitimate questions to be answered in making its application.

“This is not about Ms Gichuhi, this is about the integrity of the Senate and the electoral system,” she said before the court hearing.

“It is incredibly important that the validity of each senator’s election is beyond question.”

It is understood Labor believes it now has no practical option for continuing the legal challenge.